Firefox no longer works with some versions of Windows XP
Windows XP Service Pack 1 no longer meets the Firefox system requirements. Service Packs 2 and 3 are still supported. Let's verify that you are using Service Pack 1 or below, then explain what to do if you are.
How to check which Windows XP Service Pack is installed on your computer
- Click on the Windows button and open the Control Panel.
- Click on the Performance and Maintenance link, then click on System to open the System Properties window.
- In the System Properties window, select the General tab. Within the information in the General tab, it will tell you which service pack is installed (if one is installed).
Does it say Service Pack 2?
Try visiting the article: How can I get the latest version of Firefox on Windows XP or Vista?
Does it say Service Pack 1 or nothing at all?
The only popular web browser that is still being updated with security patches for Windows XP Service Pack 1 is Opera.
To install Opera, visit the Opera website.